Jimmy Savile abused up to 1,000 children on BBC premises, a report will claim.
An inquiry led by Janet Smith, a former British court of appeal judge, is expected to find the corporation turned a blind eye to the former DJ and presenter's offending, allowing him to rape and sexually assault hundreds of victims over five decades.
It is feared the true extent of Savile's abuse may never be known because of a culture of ignorance which "protected" him. Ms Smith is expected to say BBC executives knew about Savile's crimes, but took no action.
Peter Saunders, the chief executive of the National Association for People Abused in Childhood (NAPAC) charity, which has been consulted on the inquiry, said: "I think the 1,000 figure is based on 50 years of him offending. It has been said that he didn't have a quiet day in his life.
"There wasn't a day when he wasn't up to something, so 1,000 might not be far from the truth."
NAPAC provided support to Savile's victims, some of whom gave evidence to Ms Smith, who previously led the inquiry into the murders committed by Dr Harold Shipman.
Mr Saunders said those who passed up the opportunity to report the entertainer simply allowed him to continue his predatory offending.
He said: "I have heard a lot over the last 18 months and talked to Jimmy Savile's victims, and I have lost count of the number of people who have said they knew about the nature of the man. Margaret Thatcher was advised not to give him a knighthood due to his offensive behaviour. What did she do? She ignored it. Savile was protected by the establishment."
The scandal shook the BBC after it emerged a 'Newsnight' report into abuse by Savile was dropped, and the reasons given for doing so by its editor proved to be inaccurate.
The corporation's world editor John Simpson told the 'Andrew Marr Show' how he worked at the corporation at the same time as Savile, but dismissed the suggestion that knowledge of his offending was widespread.
"I was working all through that time," he said. "I remember what a sleaze-bag, nasty piece of work Savile was.
"But it didn't occur to me that this was going on. Of course something should have been done, and of course the BBC should have revealed it about itself."
A BBC spokesman said the corporation would not comment until the review had been published.